Thanks for posting the part numbers. Instead of "exhaust manifolds", I meant the exhaust pipes that attach to the manifolds and head rearward to the ball joint joint in the pipe under the front floor. My apologies if I did not convey that thought.
With regard to the trans cooler lines, let me put it this way . . . as the engine block castings and transmission cases most probably were the same whether in A, B, C, E, or Y-body Chrylser products, there will be a certain assembled relationship in the length from, say, the front of the block to where the cooler lines attach to the trans case. As I mentioned, if the core support of the Imperial body in the 1970s era is positioned farther away from the front of the engine (requiring a longer fan shroud as there is a particular relationship that must be maintained between the fan and the back of the shroud for optimum efficiency), then the radiator will be farther forward and necessitate longer cooler lines than on a regular C-body vehicle or any type. The deeper fan shroud would be an indicator of that plus a longer dimension from the firewall to the radiator.
If the dimension between the rear of the motor and the firewall is increased on an Imperial from the Chrysler C-body and the radiator shroud is not any deeper, then the engine would be more forward with relationship to the body and the cooler lines would most probably be the same (except possibly in the case of the isolated K-frame on the '67 era Imperials) as a regular Chrysler.
Typically, there is also a spatial relationship of the #1 spark plug and the position of the front wheel center. That relationship would be important as it would also relate to torsion bar length specifications. I strongly suspect that as the front floorpans are the same, the mounting pads for the subframe will be in the same place for C and Y-body vehicles. If the wheelbase difference is due to the front wheels being more forward, the torsion bars would be longer too, I suspect. Again, factory part numbers would not be a good guide as one extra hole being drilled for some reason or another or even a different paint/corrosion treatment would dictate a different factory part number even though the stampings are the same and will go in the exact same place.
With respect to the exhaust system items, I found those things in a Walker Exhaust Catalog for factory-configured replacement pipes. On the factory part number pipes, just one additional or less kink will generate a different factory part number just as a different material will. But a different flange angle will be different in any catalog if that is a difference between years.
Full size chassis Chrysler mufflers were typically of the same shell length for many years. The one main exception would be the 1969 440/375 Polara that used the shorter Street Hemi muffler for that one year (this was also the year that such a Polara with a 2.76 rear axle set a top speed record in the Michigan State Police tests that was not broken until the Camaro 5.7L TPI police package came out in the later 1980s). Also, the muffler used in the 1974 Imperial has the same restriction as those Street Hemi mufflers, but is "C-body sized", quiet, and has 2.5" inlet and outlet pipe diameters. One of Chrysler's little upgrades to help the Imperial engine be a better air pump.
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